Circuit for a transmission shaft rotation sensor

ABSTRACT

A circuit for use with an apparatus such as a tractor having an output device such as a mower deck or snow thrower, comprising a user operated switch and a position sensing switch to detect the rotational direction of a shaft such as an output axle, so that the operational status of the output device may be changed depending on the rotational direction of the shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application and claims the benefit ofU.S. patent application Ser. No. 10/364,237 filed on Feb. 11, 2003,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a cutoff switch for a mower blade or otherpowered device of a vehicle such as a tractor. The invention herein isdisclosed in connection with a tractor using an integrated hydrostatictransaxle as the preferred embodiment. It will be understood that thisinvention can be used with any transmission or transaxle where thedirection of travel is based on rotation of a shaft.

SUMMARY OF THE INVENTION

The invention disclosed herein comprises a reverse cutoff switch thatmay be used to disconnect power to a mower blade clutch or other deviceor vehicle system whenever the vehicle is switched into reverse. By wayof example, but not limitation, this system could be used with a backupwarning system to generate a visual and/or auditory signal that thevehicle is in reverse, or with a snow thrower to switch off the snowthrower blades when the vehicle is moving in reverse. In the preferredembodiment, the switch device is located internal to the transaxle andrelies on the actual rotation of a gear train shaft or output axle shaftto define reverse movement of the vehicle.

Most of the embodiments described herein show a switch which istriggered when the transmission or axle shaft rotates in the reversedirection, in order to disable a vehicle system or output device (suchas the mower blade) when the vehicle is moving in reverse. It will beunderstood, however, that it may be desired to have the switch triggeredwhen the axle shaft is rotated in forward to activate or deactivate anappropriate vehicle system. Such an embodiment of this invention is alsodescribed and shown herein.

Other benefits and objects of this invention are disclosed herein andwill be obvious to readers of ordinary skill in the art. The featuresdisclosed herein can be combined to create a unique design; it isunderstood, however, that such features are unique in their own rightand can be used independently with other transmission transaxle orvehicle designs, as will be obvious to one of ordinary skill in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a vehicle including a transaxleincorporating the present invention.

FIG. 2 is a top plan view of the hydrostatic transaxle shown in FIG. 1.

FIG. 3 is a side elevational view of a portion of the hydrostatictransaxle shown in FIG. 2 with certain portions, including one sidehousing, removed for clarity.

FIG. 4 is a side elevational view of the hydrostatic transaxle shown inFIG. 2, with additional elements removed for clarity.

FIG. 5 is a detail view of a switch in accordance with one embodiment ofthis invention, with the switch in the “on” position.

FIG. 6 is a detail view of the switch shown in FIG. 5, with the switchin the “off” position.

FIG. 7 is a detail cross-sectional view of an output axle and switch,along the lines A—A of FIG. 4.

FIG. 8 is a cross-sectional view similar to that of FIG. 7 of a secondembodiment of a switch in accordance with the present invention.

FIG. 9 shows a detail view of another embodiment of a switch inaccordance with the present invention, with the switch in the “off” or“open” position.

FIG. 10 shows a detail view of another embodiment of a switch inaccordance with the present invention, with the switch in the “off” or“open” position.

FIG. 11 shows a detail view of the switch shown in FIG. 10, with theswitch in the “on” or closed position.

FIG. 12 is a detail view of a switch in accordance with a fifthembodiment of this invention.

FIG. 13 is a detail, partial cross-sectional view of a switch inaccordance with a sixth embodiment of this invention.

FIG. 14 is a schematic of an electric circuit in accordance with thepresent invention.

FIG. 15 is a flow chart of the schematic shown in FIG. 14.

FIG. 16 is a detail, partial cross-sectional view of a switch inaccordance with a seventh embodiment of this invention, where the switchis triggered in the forward instead of the reverse directions.

FIG. 17 is a schematic view of the electric circuit of the seventhembodiment of the invention shown in FIG. 16.

FIG. 18 is a flowchart of the embodiments shown in FIGS. 16 and 17.

FIG. 19 is a schematic of an electric circuit in accordance with anotherembodiment of this invention.

FIG. 20 is a flowchart of the embodiment depicted in the schematic shownin FIG. 19.

FIG. 21 is a schematic of an electric circuit in accordance with yetanother embodiment of this invention, similar to that shown in FIG. 19.

FIG. 22 is a flowchart of the embodiment depicted in FIG. 21.

FIG. 23 is a schematic of an electric circuit in accordance with yetanother embodiment of this invention.

FIG. 24 is a flowchart of the embodiment depicted in FIG. 23.

DETAILED DESCRIPTION OF THE DRAWINGS

As noted above, this invention is described herein with respect to avehicle including an integrated hydrostatic transaxle, but it will beunderstood that this invention is not limited to such an application.Multiple embodiments of this invention are depicted in the figures anddescribed below. Identical structure in the different embodiments isgiven identical numerals throughout; where appropriate, differentprefixes are used to differentiate between structure that is similar butnot identical.

FIG. 1 shows a typical vehicle 11 having an engine 29 mounted on avehicle frame 31, rear drive wheels 16 and front steering wheels 17; oneof the wheels 16 and 17 have been removed from this figure for clarity.A hydrostatic transaxle 10 is mounted towards the rear of the vehicle topower both drive wheels 16 by means of a belt drive system 21 which alsopowers a mower deck 80 through a clutch 92. All of these elements andthe interconnections therebetween are well-known in the art and will notbe described in detail. Transaxle 10 is shown in more detail in FIGS.2-4; this transaxle depicted herein is very similar to that shown inU.S. Pat. No. 6,253,637, the terms of which are incorporated herein byreference.

The operation of transaxle 10 is also well known and will not bedescribed in detail herein. The hydrostatic transaxle compriseshydraulic and gear elements located inside a housing formed by casingmembers 24 and 26. A hydrostatic pump assembly 14 is mounted on a centersection 20 and driven by input shaft 12. Swash plate apparatus 13 ismoved by means of trunnion 25 and controls the output of pump cylinderblock 23, which controls the speed and direction of a hydraulic motor(not shown), which in turn drives motor shaft 22.

Power is transmitted through a gear train 27 including a reduction gearshaft 15 to a differential 28, which in turn drives output axles 30. InFIG. 4, various gears and bearings are removed so that the location ofthe invention in this embodiment may be more clearly seen. While theswitch configuration depicted herein is located on axle shaft 30 in thisembodiment, it could also be located on other shafts such as motor shaft22 or reduction gear shaft 15.

FIGS. 5-7 show detail views of this first embodiment, where switchactuator 34 is mounted on axle 30 and is rotatable therewith. Washers 32may be used to properly locate actuator 34. A sensor such as proximityswitch 36 is mounted in the transaxle casing member 24 and lead 37extends outwardly therefrom. Switch actuator 34 has a limited range ofmovement, as shown in FIGS. 5 and 6. Surface 40 is formed on actuator 34and as actuator 34 rotates clockwise in these figures, which correspondsto the forward direction of axle 30, surface 40 will contact stops 44 toprevent further rotation of actuator 34. Friction means 38, which isdepicted herein as a gasket, may be interposed between switch actuator34 and axle shaft 30 to permit actuator 34 to move with respect to axleshaft 30 while being stopped with respect to casing member 24. Frictionmeans 38 is preferably a gasket made of a material such as Nitrile orpolyacrylate with a hardness of 50 to 90 durometer, although otherfriction devices using materials such as leather, brake pad material orthe like may be used depending on the application requirements.

When axle shaft 30 moves into the reverse direction, actuator 34 isrotated into the position shown in FIGS. 5 and 7. This rotation isenhanced by the frictional force between actuator 34 and friction means38 and between axle shaft 30 and friction means 38. Proximity switch 36is then actuated by the proximity of surface 35 on actuator 34. Asbefore, the rotational movement of actuator 34 is stopped by contact ofsurface 42 with stop 46, whereupon friction means 38 will allow movementof the axle shaft 30 relative to actuator 34.

Proximity switch 36 may be one of a variety of such switches, such as amagnetic or inductive switch. If an inductive switch is used, surface 35needs to be metal. If a magnetic switch is used, surface 35 will need tobe configured to accommodate a magnet to be located thereon.

A second embodiment of this design is shown in FIG. 8, which includes aunidirectional bearing 48 located between actuator 134 and axle shaft30; as in the earlier embodiment, actuator 134 acts to trigger proximityswitch 36. The inner diameter of actuator 134 needs to be shaped toaccommodate bearing 48, and washers 132 are used to properly locateactuator 134, with friction means 138 mounted between the outer diameterof bearing 48 and an inner diameter of actuator 134. Bearing 48 helps toreduce wear of friction means 138 because bearing 48 rotates relativelyeasily against axle shaft 30 when actuator 134 contacts the forward stopin casing member 24, and the frictional force between unidirectionalbearing 48 and actuator 134 caused by contact with friction means 138will hold unidirectional bearing 48 fixed with respect to actuator 134.When axle shaft 30 rotates in reverse, bearing 48 locks against axleshaft 30 and rotates therewith. When actuator 134 hits a stop, frictionmeans 138 allows actuator 134 to remain fixed while axle shaft 30 andbearing 48 rotate.

It is preferred to use proximity switches as described above so that theswitch can be actuated with the minimum force possible, due to thelimited resistance to movement of the gasket interface. Proximityswitches are also long-lived, which can be an important benefitdepending on the application. However, such proximity switches can alsobe expensive and in certain applications it may be preferred to use aless expensive alternative.

One such alternative is shown in FIG. 9, where a mechanical switch 236is used as the sensor. Specifically, mechanical switch 236 has twocontacts 52 and 54, mounted therein and extending downwardly therefromtowards actuator 234. Actuator 234 is composed of an electricallynon-conducting material. A generally U-shaped metal contact 50 isfastened to actuator 234 by means of fastener 56. When axle shaft 30rotates into the forward position (as shown in FIG. 9), surface 240 willcontact stop 244, and contact 50 will not contact any conductingelements. When axle shaft 30 rotates in the opposite, or reverse,direction, surface 242 will engage stop 246 so that the two flexiblearms of contact 50 simultaneously touch contacts 52 and 54 to close anelectrical circuit, closing switch 236, thus indicating that axle shaft30 has rotated in the reverse direction.

A fourth embodiment, which is similar in many aspects to the embodimentshown in FIG. 9, is shown in FIGS. 10 and 11. Switch 336 includes a pairof contacts 60 and 64 extending downwardly therefrom. Contact 60 isflexible and is shaped to move in and out of contact with contact 64.Contact 60 preferably has a flexibility which is significantly less thanthe force required to permit relative rotation between actuator 334 andaxle shaft 30 by slippage of the friction means in the interface betweenaxle shaft 30 and the actuator 334. As can be seen in FIG. 10, when axleshaft 30 rotates into the forward position, surface 340 of actuator 334moves into contact with stop 344, and contacts 60 and 64 do not touch.When axle shaft 30 moves in the reverse direction, surface 62 ofactuator 334 will push contact 60 into contact 64, completing anelectrical circuit and thus closing switch 336. Movement of actuator 334in the reverse direction is limited by the interaction of surface 342 onactuator 334 with stop 346, to limit the potential of damage to flexiblecontact 60. It will be understood that in this embodiment as well as theother embodiments discussed herein that the shape and location of thevarious actuator surfaces and stops that interact to limit rotationalmovement of the actuators may be modified to fit the application.

Other means of stopping rotation of the actuator and/or actuating theswitch will be obvious to one of skill in the art. By way of example, afifth embodiment is shown in FIG. 12, where a low actuation force switchplunger 58 is mounted in switch body 436. Rotation of axle shaft 30 inthe forward direction moves actuator 434 to the position shown in FIG.12, where surface 440 contacts stop 444 to limit the forward rotation ofactuator 434. When axle 30 rotates in the reverse direction, surface 442contacts plunger 58, which both triggers switch 436 and limits furtherrotation of actuator 434.

A sixth embodiment is shown in FIG. 13 which is very similar inoperation to that shown in FIG. 12. Switch 536 includes a pair ofcontacts 68 and 70 which are spring loaded with low force springs 74.Rotatable actuator 534 is composed of a non-conductive material such asplastic. Its rotational movement is limited in a manner similar to thatdescribed above with respect to FIG. 12. Actuator 534 includes metalcontact or pad 72 placed thereon in a manner and location such that whenactuator 534 rotates in the reverse direction, pad 72 contacts bothcontacts 68 and 70 to close the electrical circuit and trigger theswitch as described above.

FIG. 14 is a schematic circuit diagram 1000 of a reverse blade cutoffswitch constructed according to one embodiment of the present invention.Any of the proximity switches described above, such as switch 36, iscoupled between a blade momentary switch 84 and a relay 90 as shown indiagram 1000. When the operator wishes to stop operation of the mowerblades 94, momentary switch 84 may be depressed so that contacts 84B inswitch 84 are no longer connected, which then causes latching relay 88to be released or deactivated. The purpose and functionality ofmomentary switch 84 is described in greater detail below. The latchingrelay 88 is coupled to a blade clutch 92 which controls blades 94 inmower deck 80. A battery 82 is coupled to several nodes in the circuit,as shown FIG. 14.

In FIG. 14, a brake switch 86 is coupled between blade momentary switch84 and latching relay 88 as shown in the circuit diagram 1000. Brakeswitch 86 is beneficial in hydrostatic transaxle applications where theprimary means of braking the transaxle is the hydraulic braking thatoccurs as the swash plate nears neutral. In these embodiments, brakeswitch 86 is included to cause release of latching relay 88 in the eventthe brake is actuated, which is seen as an operational advantage in thatthe conditions that would cause the actuation of a brake in ahydrostatic application would also likely benefit from blades 94 beingdisengaged. In other embodiments involving transaxles where the primarymeans of braking is a dynamic brake, brake switch 86 may not be desiredand can be omitted such that blade momentary switch 84 is coupleddirectly to latching relay 88. Another option may be to include switch86 as a part of the parking brake function of such transaxles. As with ahydrostatic transaxle, the operational benefit is that any conditionwhich requires activation of the parking brake would likely benefit fromdisengagement of the blades 94.

FIG. 15 is a flow diagram 100 which shows the functionality of thecircuit of FIG. 14. In step 1102, when the operator releases the brake,the brake switch 86 is closed. Continuing with step 1104, the blademomentary switch 84 is actuated so that contacts 84A allow a voltagesignal to reach and actuate latching relay 88, also referred to hereinas a self-holding relay. The process proceeds to step 1106 in which itis determined whether the axle shaft has rotated in reverse. When theaxle shaft rotates in reverse, in step 1108, switch 36 is closed,causing relay 90 to actuate, removing voltage from blade clutch 92,causing blades 94 to be disengaged. To this end, blade clutch 92preferably includes a brake to stop movement of the disengaged blades94.

In FIG. 15, after the blades 94 are disengaged in step 1108, it isdetermined in step 1110 whether the axle has rotated out of reverse. Instep 1110 or 1106, when the axle has rotated out of reverse, switch 36responds by opening in step 1112 to deactivate relay 90, such thatvoltage is returned to blade clutch 92 to engage blades 94. In step1110, if the axle has still not rotated out of reverse, control proceedsto step 1116. In steps 1114 and 1116, when the brake is actuated, theprocess proceeds to step 1122 in which brake switch 86 opens, causingrelease of latching relay 88 thus removing power from clutch 92 to stopthe blades 94. In steps 1114 and 1116, when the brake is not actuated,the process continues to steps 1118 and 1120 to determine whether theblade momentary switch 84 has been actuated by the operator tode-energize the self-holding relay. When momentary switch 84 has beendepressed, in step 1122 latching relay 88 is deactivated, thus removingpower from clutch 92 to stop the blades 94. When the blade momentaryswitch has not been depressed, control returns to step 1106 or 1110 toagain determine whether the axle is rotating in the reverse direction.

FIG. 16 shows a seventh embodiment of this invention where the switch636 is triggered when axle 30 is rotated in the forward direction asopposed to the reverse direction. This embodiment is otherwise identicalto that shown in FIG. 12 and the same description therein will apply.Specifically, rotation of axle 30 in the forward direction would causesurface 640 to contact plunger 58 to close switch 636. Rotation ofactuator 634 in the reverse direction is limited by the interaction ofsurface 642 with stop 646.

FIG. 17 is a schematic circuit diagram 1200 of a reverse blade cutoffswitch constructed according to the seventh embodiment of the presentinvention. The circuit of FIG. 17 corresponds to the embodiment of FIG.16, where the switch is triggered in the forward instead of the reversedirection. The circuit diagram 1200 of FIG. 7 is nearly identical tothat of FIG. 14; the difference is that relay 91 of diagram 1200replaces relay 90 of diagram 1000, and relay 91 is wired as illustratedin FIG. 17 such that relay 91 is activated when the axle moves into theforward position rather than the reverse position. The configuration ofFIG. 17 provides the advantage that if the circuit fails, the blades 94will not be activated, or if activated, they will be deactivated.

FIG. 18 is a flow diagram 1300 which shows the functionality of thecircuit of FIG. 17. In step 1302, the brake is released such that brakeswitch 86 is closed. In step 1304, the blade momentary switch 84 isactuated to energize the self-holding relay, that is, latching relay 88in FIG. 17. The process proceeds to step 1306 in which it is determinedwhether the axle is in a forward, rather than a reverse, position. Whenthe axle shaft is not rotating forward, in step 1308, switch 36 is openand clutch 92 is inoperative such that blades 94 are stopped or remainstopped. After step 1308, it is again determined in step 1310 whetherthe axle has rotated in a forward direction. In step 1310 or 1306, whenthe axle has rotated forward, closing switch 36, control proceeds tostep 1312 in which relay 91 is actuated, causing clutch 92 to beenergized so that blades 94 operate. In step 1310, if the axle has stillnot rotated forward, control proceeds to step 1316.

In steps 1314 and 1316 of FIG. 18, when the brake is actuated, the brakeswitch 86 opens to remove voltage from latching relay 88, in step 1322,thus removing power from clutch 92 to stop the blades 94 or to keepblades 94 stopped. In steps 1314 and 1316, when the brake is notactuated, control proceeds to steps 1318 and 1320 to determine whetherthe blade momentary switch 84 has been actuated by the operator tode-energize the self-holding relay. When momentary switch 84 has beenactuated, control proceeds to step 1322 in which latching relay 88 isdeactivated, thus removing power from clutch 92 to stop the blades 94 orto keep blades 94 stopped. If the blade momentary switch is notactuated, control returns to step 1306 or 1310 to again determinewhether the axle is rotating in the forward direction.

FIG. 19 is a schematic circuit diagram 1400 showing another embodimentof a reverse blade cutoff switch constructed according to the presentinvention. The circuit of FIG. 19 incorporates several of the circuitelements of FIGS. 14 and 17. In addition, the circuit of FIG. 19includes a time delay circuit 100, a relay 102, a handle switch 98, anda relay 96 in place of relays 90 and 91.

FIG. 20 shows a flow diagram 1500 which demonstrates the functionalityof circuit 1400. In step 1502, the brake is released so that brakeswitch 86 is closed. In step 1504, blade momentary switch 84 is actuatedso that latching relay 88 is energized. In step 1506, it is determinedwhether the axle has rotated in reverse. When the axle shaft rotates inreverse, in step 1508, switch 36 is closed, activating relay 96.Activation of relay 96 removes voltage from contacts 88A of latchingrelay 88, thereby removing power from clutch 92, causing blades 94 tostop. In step 1506, when the axle has not rotated in to reverse, theswitch 36 remains open. Thus, in step 1510, clutch 92 remains energizedso that blades 94 can operate.

In steps 1512 and 1514 of FIG. 20, when the control handle or pedal ofthe vehicle is in a position inconsistent with the direction of axleshaft 30 rotation, such as forward or neutral while axle shaft 30 is inthe reverse position, switch 36 and handle switch 98 will be closed.Voltage will be applied through time delay circuit 100, which will thenactuate relay 102 if axle shaft 30 has not rotated out of reverse duringthe time delay, which will then cause deactivation of latching relay 88.Thus, if the operator wishes to continue mowing when such a conditionoccurs, the operator will need to cause axle 30 to rotate out of reverseand then actuate momentary switch 84 again to reengage the mower blades.This configuration thus provides an additional safety feature formowing.

In FIGS. 19 and 20, given that switch 36 may be closed while shiftinginto a forward position, and it may take some period of time for switch36 to open, the resulting need to reengage momentary switch 84 forroutine operations such as forward and reverse maneuvering would be anannoyance for most operators. Thus, time delay circuit 100 is providedto allow time for switch 36 to become open during a shift from reverseto forward. While the range of time may be chosen as desired, based onthe expected application, the preferred time delay is between 2 and 4seconds. After this predetermined time delay, if switch 36 remainsclosed and handle switch 98 remains closed, then latching relay 88 willde-activate, requiring the operator to reengage switch 84 to continuemowing.

In FIG. 20, the time delay provided by delay circuit 100 begins in step1514. During the delay period, control proceeds through a sequence ofsteps 1516-1524. In step 1516, it is determined whether the axle remainsin reverse. When the axle is not in reverse, control proceeds to step1510 described above. When the axle is in the reverse position, controlproceeds to step 1518 to determine the status of the brake. When thebrake has been actuated, brake switch 86 opens to cause deactivation oflatching relay 88, in step 1526, thus removing power from clutch 92 tostop the blades 94. In step 1518, when the brake is not actuated,control proceeds to step 1520 to determine whether the blade momentaryswitch 84 has been actuated by the operator. When momentary switch 84has been actuated, control proceeds to step 1526. When the blademomentary switch is not actuated, control proceeds to step 1522 to againdetermine whether the control handle or pedal is in an inconsistentposition such as forward or neutral. If the control handle or pedal hasbeen returned to reverse, then control proceeds to step 1530, whichfunctions as described in the next paragraph. When in the forwardposition, in step 1524, it is determined whether the pre-determined timeof delay circuit 100 has expired. If this delay period has not expired,control returns to step 1516 to repeat steps 1516-1524. In step 1524,when the time delay has expired, control proceeds to step 1526.

In steps 1528 and 1530 of FIG. 20, when the brake is actuated, controlproceeds to step 1526. When the brake is not actuated, control proceedsto step 1532 or 1534 to determine whether the blade momentary switch 84has been actuated by the operator. When the blade momentary switch isnot actuated, control returns to step 1506 from step 1532, and to step1512 from step 1534. In steps 1532 and 1534, when the blade momentaryswitch 84 is actuated to de-energize the latching relay 88, the blades94 stop or remain stopped in step 1526.

FIG. 21 is a schematic circuit diagram 1600 showing another embodimentof a reverse blade cutoff switch constructed according to the presentinvention. FIG. 22 shows a flow diagram 1700 which demonstrates thefunctionality of circuit 1600. FIGS. 21 and 22 are very similar to FIGS.19 and 20, except with the addition of a reverse cutoff bypass switch104 coupled as shown in FIG. 21. Switch 104 is preferably mounted in alocation easily accessible to an operator, such as a part of thetransaxle hand control, mounted to the floor of the vehicle or asteering wheel mounted switch. If the operator believes that during areversing operation relay 88 might become disengaged, and conditionspermit allowing the blades 94 to operate while performing a reversingoperation, the operator may depress switch 104, in step 1702 of FIG. 22,to maintain actuation of relay 88 during a reversing operation andsubsequent movement forward.

While the above electrical schematics describe configurations using ablade clutch 92, such clutches are expensive and add complexity to amower. Many current safety systems work by shutting off the vehicleengine or preventing the engine from starting when a predetermined stateis achieved. An embodiment of the current invention in such aconfiguration is shown in FIGS. 23 and 24.

The schematic circuit diagram 1800 shown in FIG. 23 uses a switch 10,which could be a part of the blade engagement mechanism, and switch 36.Switch 110 is used to determine whether it is safe to start vehicleengine 29, and switches 110 and 36 are used to determine whether it issafe to continue operation of vehicle engine 29. When ignition switch106 is rotated to engage contact 106B, a voltage signal is then directedto contacts in switch 110. If the blade engagement mechanism is in thedisengaged position, the voltage signal is then connected to the enginestart circuit 112, as shown, to allow the engine to be started. Onceengine 29 has been started and ignition switch 106 is released so thatcontact 106A is engaged, a voltage signal will be passed through relay114 to a circuit 116. Circuit 116 is preferably an engine-run enablecircuit that permits the engine to keep operating. In some mowerapplications, circuit 116 will be associated with various safetyswitches such as the seat, brake or other elements not shown, which, ifset into a predetermined position, may also cause vehicle engine 29 tobe turned off.

In the circuit shown in FIG. 23, if axle shaft 30 rotates into reverse,then switch 36 will close to send a voltage signal to switch 110. If themower blades are engaged, switch 110 will be switched opposite theposition shown in FIG. 23 to connect voltage through contact 110A, thusenergizing relay 114 and consequently removing a voltage signal fromengine-run enable circuit 116, which will then cause vehicle engine 29to be turned off. There is also an optional reverse cutoff bypass switch104 which may be actuated if the operator specifically wants to avoidhaving engine 29 turned off, so that the user can allow blades 94 tooperate while the vehicle is in reverse. Actuating switch 104 opensswitch 104 so that a voltage signal that might otherwise actuate relay114 due to the actuation of switch 36 and switch 110 will be preventedfrom doing so.

FIG. 24 shows a flow diagram 1900 describing the functionality ofcircuit 1800. In step 1902 the operator operates ignition switch 106 tostart engine 29. The process proceeds to step 1904 where it isdetermined whether the mower blade engagement mechanism is in theengaged position. If that handle is in the engaged position, then theprocess terminates with step 1906 because the engine will be preventedfrom starting. If the mower blade engagement mechanism is in thedisengaged position the process will proceed to step 1908 where engine29 starts. Once engine 29 starts, the operator will allow ignitionswitch 106 to move to the run position. In step 1910 the operatorengages the mower blades 94. In step 1912 it is determined whether axleshaft 30 has rotated into the reverse position. If the axle shaft 30 hasrotated into reverse, then the process will either move to step 1916 inwhich engine run circuit 116 is commanded to shut engine 29 down, or ifa reverse cutoff override switch 104 is available, the process willdetermine whether that switch has been engaged. If switch 104 has notbeen engaged, then the process will continue on to step 1916 and engine29 will be stopped. If switch 104 has been engaged, then the processwill move to step 1918 and mower blades 94 will be allowed to operate.The process then determines whether blades 94 are disengaged; if blades94 are not disengaged, then the process returns to step 1912. If blades94 are disengaged, then the operator is free to turn off the engine atany time to cease operation at step 1922.

While specific electronic schematics and flow charts have been presentedto describe certain exemplary embodiments of this invention, thoseskilled in the art will recognize that such schematics and flow chartsmay be accomplished in a variety of implementations using a variety ofcomponents that accomplish essentially the same function, and thus thedisclosed schematics and flow charts are only representative and are notintended to be limiting.

The embodiments disclosed herein depict a hydrostatic transmission,where the various components are located in a common sump. The hydraulicoil used in such hydrostatic transmissions or transaxles has anegligible electrical conductivity; it will also be understood thatappropriate seals will be required for the various componentspenetrating the housing in such a device, such as switch 36. Thisinvention could also readily be used in mechanical transmissions ortransaxles.

Those skilled in the art should understand that various commerciallyavailable switches can be used to implement the proximity switchesdescribed above. Suitable switches include inductive proximity switches,magnetic proximity switches, and low actuating force switches. Exemplaryinductive proximity switches include models made by Honeywell, and thePRX 800 series available from Sacramento Electronic Supply. Exemplarymagnetic proximity switches include the MS-20 proximity switch availablefrom Rodale Technical Sales, Inc. and models made by Jackson Research,Ltd. A suitable low actuating force switch is manufactured byVeeder-Root. The switches used must be suitable for the expectedoperating environment.

It is to be understood that the above description of the inventionshould not be used to limit the invention, as other embodiments and usesof the various features of this invention will be obvious to one skilledin the art. This invention should be read as limited by the scope of itsclaims only.

1. In an apparatus having an output device with an operational status, atransmission including an input driven by a prime mover and a shaftdriven by the input, a circuit for controlling the operational status ofthe output device depending on a rotational direction of the shaft, thecircuit comprising: a user actuated switch responsive to user input; aposition sensing switch positioned to detect the rotational direction ofthe shaft, the position sensing switch being actuated when the shaftrotates in one of a forward direction and a reverse direction; a firstrelay having an input and an output, the first relay input coupled tothe position sensing switch, the first relay being actuated responsiveto actuation of the position sensing switch; and a second relay having afirst control input, a second control input, and an output, the firstcontrol input coupled to the user actuated switch, the second controlinput coupled to the first relay output, the second relay output coupledto the output device, the second relay controlling the operationalstatus of the output device between an engaged state and a disengagedstate responsive to actuation of the user actuated switch, andresponsive to actuation of the first relay.
 2. The circuit of claim 1further comprising: a brake switch coupled between the user actuatedswitch and the first control input of the second relay, the second relaycausing the output device to be in the disengaged state responsive toactuation of the brake switch.
 3. The circuit of claim 1, the positionsensing switch being actuated when the shaft rotates in a reversedirection.
 4. The circuit of claim 3, the second relay causing theoperational status of the output device to be in the disengaged stateresponsive to the position sensing switch being actuated.
 5. The circuitof claim 1, the position sensing switch being actuated when the shaftrotates in a forward direction.
 6. The circuit of claim 5, the secondrelay causing the operational status of the output device to be in theengaged state responsive to the position sensing switch being actuated.7. The circuit of claim 1, wherein the apparatus comprises a vehicle,and the output device comprises a blade clutch controlled by the secondrelay.
 8. The circuit of claim 7, the output device further including ablade driven by the blade clutch.
 9. The circuit of claim 1, the secondrelay causing the output device to be in the disengaged state responsiveto actuation of the user actuated switch.
 10. The circuit of claim 1,wherein the user actuated switch is a momentary switch.
 11. The circuitof claim 1, wherein the position sensing switch is a proximity switch.12. The circuit of claim 1, wherein the position sensing switch isactuated responsive to mechanical contact.